SPINE

SPINE is a methhod to detect in vivo protein-protein interactions

A detailed protocol to detect the interaction between RocG and GltC:

1 litre of a Bacillus subtilis culture was grown to an OD600 of approx. 1.0 and incubated with 0.6% formaldehyde (stock solution 4% in PBS, pH 6.5!) for 20 minutes @ 37°C on a shaker. The cells were harvested and washed once in 1 X PBS pH 6.5. The pellets can then be stored @ -20 °C. The GltC protein was expressed carrying a Strep-tag and RocG expression was induced by arginine (see Commichau et al., 2007 Mol Microbiol). Expression of the Strep-tagged GltC protein allows to test the functionality of the protein. Crude extracts (10-15 ml) were prepared by using a French Press. After a centrifugation step for 1 h @ 27.000 g the clarified crude extracts were loaded onto a Streptactin sepharose column (0.5-1 ml matrix) to isolate the cross-linked protein complexes (the detailed procedure for protein purification is described in the IBA manual, http://www.iba-go.com/). After the purification of the protein complexes the crosslinks can be resolved by boiling the samples in laemmli buffer for 10-15 minutes @ 95 °C (Herzberg et al., 2007 Proteomics). A 12.5% SDS gel was loaded with the samples and the proteins were then visualized by silver-staining. We identified the interaction partner/s by mass spectroscopy and Western blotting.

Preparation of the formaldehyde stock solution (max. 4% in 1X PBS pH 6.5): We use paraformaldehyde (a white powder). Paraformaldehyde can be solved in 1 X PBS for approx. 20-30 minutes @ 65 to 70 °C.

The sepharose matrix was purchased from the IBA company, Göttingen (http://www.iba-go.com/).